Not to get too far off the topic, but since it's the OP talking...
Where's the AIS coming from? I have setup pretty much the same except I use PolarNavy on the PC (dell mini notebook that runs on a 100w inverter
with a GPS
puck I got for 15 bucks), and its a backup at the nav station inside.
I use my SH 2150x VHF
for the AIS, works like a charm.
And yes, the area Towboat US skippers are not following the policy; no checks on DSC.